There are many different types and kinds of exercise machines as a review of the issued U.S. patents can attest. Most of these devices are designed to provide either a constant resistance throughout the exercise motion or a variable resistance that varies according to a fixed resistance curve. The resistance curve is fixed for each of these exercise devices and the shape of the resistance curve cannot be varied. Such devices are disclosed in U.S. Pat. Nos.: 4,799,670; 4,666,149; 4,635,933; 4,502,681; 4,500,089; 4,494,751; 4,405,128; and 2,855,199.
The disadvantages with these exercise devices are particularly apparent in U.S. Pat. Nos.: 4,836,536; 4,709,920; and 4,711,448. In U.S. Pat. Nos. 4,836,536 and 4,711,448 the resistance experienced by the user is constant throughout the range of motion of the exercise. Consequently, the resistance curve for each of these devices is fixed and cannot be changed. In U.S. Pat. No. 4,709,920, the resistance experienced by the user varies throughout the range of motion of the exercise due to the use of a cam path which has a varying radius. The resistance curve for this device, however, is fixed due to the shape of the particular cam path chosen. While the cam path and thus the resistance curve, can be varied somewhat by shifting the orientation of the intermediate support using holes and locking pins, one can only select between a limited number of cam paths and thus a limited number of resistance curves. Moreover, due to the preset arrangement of the holes and the intermediate support, the number of cam paths and thus the number of resistance curves to choose from is limited for any given embodiment of this device. Only by changing the intermediate support or using a different arrangement of holes can a wider range of resistance curves be implemented.
Most existing exercise devices provide but a single resistance curve that cannot be altered. Some, however, enable the resistance curve to be varied, but the choice of resistance curves is very limited. As a result, the muscular growth of the users of such devices is limited. Moreover, the inability of these exercise devices to adapt their resistance curves to the specific needs of the individuals using them causes them to be inadequate in many situations, especially where the needs of the various individual users differ significantly. These situations arise frequently in training or with injured individuals undergoing physical rehabilitation where it is desirable to provide a wide range of different resistance curves that easily can be adjusted to meet the specific needs of any individual.
It would be desirable therefore, to develop an exercise device which overcomes the problems of the present devices and provides not only a variable resistance but also a plurality of resistance curves which may be selectively chosen and easily adjusted by the user to meet his specific needs.